Ultrasound Scanner Built with Capacitive Micromachined Ultrasonic Transducers (CMUTS)

ABSTRACT

Ultrasonic scanners and methods of manufacturing ultrasonic scanners. One embodiment of a method includes integrating a flexible electronic device (e.g. an IC) and a flexible ultrasonic transducer (e.g. a portion of a circular CMUT array) with a flexible member. The IC, the transducer, and the flexible member can form a flexible subassembly which is rolled up to form an ultrasonic scanner. The integration of the IC and the transducer can occur at the same time. In the alternative, the integration of the electronic device can occur before the integration of the transducer. Moreover, the integration of the transducer can include using a semiconductor technique. Furthermore, the rolled up subassembly can form a lumen or can be attached to a lumen. The method can include folding a portion of the flexible subassembly to form a forward looking transducer. The flexible member of some subassemblies can include a pair of arms.

PRIORITY

This application claims priority from U.S. Provisional Application Ser.No. 60/992,020, filed Dec. 3, 2007 and U.S. Provisional Application Ser.No. 61/024,843, filed Jan. 30, 2008.

BACKGROUND

The present application relates to capacitive micromachined ultrasonictransducer (CMUT) scanners and, more particularly to catheters equippedwith CMUT based ultrasonic scanners.

A catheter allows surgical personnel to diagnose and treat conditionsdeep within a patient's body by navigating the distal end of thecatheter to the site where some condition might exist. Then, surgicalpersonnel can operate various sensors, instruments, etc. at the site toperform certain procedures with minimal intrusive effect on the patient.One type of sensor that has found widespread use is the ultrasonicscanner. Ultrasonic scanners generate acoustic waves at frequenciesselected for their ability to allow the acoustic waves to penetratevarious tissues and other biological structures and return echoes therefrom. Often, it is desired to select frequencies on the order of 20 MHzor higher. Images of the tissue surrounding the ultrasonic scanner canbe derived from these returned echoes. Two types of ultrasonic scannersexist, those which are based on piezoelectric crystals (i.e., a crystalfabricated from a piezoelectric material or a piezoelectric compositematerial) and those based on capacitive micromachined ultrasonictransducers (CMUTs and embedded spring CMUTS or ESCMUTs).

CMUTs typically include two spaced apart electrodes with a membraneattached to one of the two electrodes. In operation, an alternatingcurrent (AC) signal is used to charge the electrodes to differingvoltages. The differential voltage induces movement of the electrodeattached to the membrane and hence, the membrane itself. A piezoelectrictransducer (PZTs) also applies an AC signal to the crystal thereincausing it to vibrate and produce acoustic waves. The echoes returned tothe crystal are used to derive images of the surrounding tissue.

Thus, surgical personnel have found it useful to employ ultrasonicscanner equipped catheters to obtain images of certain tissues (e.g.blood vessels), structures, etc. within human (and animal) patients andto view the effects of therapy thereon. For instance, ultrasonictransducers can provide images which allow medical personnel todetermine whether blood is flowing through a particular blood vessel.

Some catheters include a single ultrasonic transducer situated at, ornear, the distal end of the catheter whereas other catheters includearrays of ultrasonic transducers at the distal end of the catheter.These ultrasonic transducer transducers can be arrange along the side ofthe catheter and can point outward there from. If so they can bereferred to as “side looking” transducers. When the catheter only hasone side looking transducer the catheter can be rotated to obtain imagesof the tissue in all directions around the catheter. Otherwise, thecatheter can have ultrasonic transducers pointed in all directionsaround the catheter.

In other situations, catheters can have ultrasonic transducers arrangedat the distal end of the catheter which point in a distal direction fromthe end of the catheter. These types of ultrasonic transducers can bereferred to as “forward looking” transducers. Forward lookingtransducers can be useful for obtaining images of tissue in front of(i.e. “forward” of) the catheter.

SUMMARY

Embodiments provide catheters equipped with ultrasonic scanners andmethods of manufacturing catheters equipped with ultrasonic scanners.More particularly, a method practiced according to one embodimentincludes integrating a flexible electronic device (e.g. an integratedcircuit) with a flexible member and integrating a flexible ultrasonictransducer (e.g. a portion of a circular CMUT array) with the flexiblemember. The integrated flexible electronic device, flexible ultrasonictransducer, and flexible member can form a flexible subassembly which isrolled up to form the ultrasonic scanner.

In some embodiments, the integration of the flexible electronic deviceand the flexible ultrasonic transducer with the flexible member occursat the same time. Furthermore, the integration of the ultrasonictransducer can be performed from the side of ultrasonic transducer whichincludes its active surface. In the alternative, the integration of theflexible electronic device can occur before (or after) the integrationof the flexible ultrasonic transducer. Moreover, the integration of theflexible ultrasonic transducer can include using a semiconductortechnique. In some embodiments, the rolled up flexible subassembly formsa lumen which can be coupled to the lumen of a catheter. However, therolled up flexible subassembly can be attached to a lumen of a catheterinstead. In some embodiments, the method includes folding a portion ofthe flexible member (which hosts the flexible ultrasonic transducer)through an angle of about ninety degrees to form a forward lookingultrasonic transducer. The flexible member of some embodiments caninclude a pair of arms attached to portions of a circular array of CMUTtransducers. As the arms (and the rest of the flexible member) arerolled up, the circular CMUT array can be folded through about ninetydegrees to form a ring shaped CMUT array. The ring shaped CMUT array canthen be used as a forward looking CMUT array.

One embodiment of an ultrasonic scanner disclosed herein includes aflexible electronic device (e.g. an integrated circuit), a flexibleultrasonic transducer; and a flexible member with the flexibleelectronic device and the flexible ultrasonic transducer integrated withthe flexible member. The integrated flexible electronic device, theflexible ultrasonic transducer, and the flexible member can form aflexible subassembly which is rolled up to form the ultrasonic scanner.In some embodiments, the rolled up flexible subassembly is a lumen or,instead, can be attached to a lumen of a catheter. The flexibleultrasonic transducer can include a through wafer interconnect and aportion of a circular CMUT array in communication therewith. Moreover,the ultrasonic transducer can be a forward looking, ring shaped CMUTarray.

Accordingly, embodiments provide many advantages over previouslyavailable ultrasonic transducer equipped catheters and, moreparticularly, over PZT equipped catheters. For instance, embodimentsprovide catheters with ultrasonic scanners which can operate at higherfrequencies and with wider bandwidths than heretofore possible.Embodiments also provide catheters with ultrasonic scanners with smallerform factors than those of previously available ultrasonic transducers.In addition, embodiments provide methods of manufacturing cathetersequipped with ultrasonic scanners which are simpler, less costly, andfaster than previously available ultrasonic catheter manufacturingmethods.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a cross sectional view of a catheter of someembodiments.

FIG. 2 illustrates cross sectional views of an ultrasonic scanner ofsome embodiments.

FIG. 3 illustrates a flow chart illustrating a method of manufacturing acatheter of some embodiments.

FIG. 4 illustrates a cross sectional view of an ultrasonic scanner for acatheter of some embodiments.

FIG. 5 illustrates a cross sectional view of another ultrasonic scannerfor a catheter of some embodiments.

FIG. 6 illustrates a cross sectional view of another ultrasonic scannerfor a catheter of some embodiments.

FIG. 7 illustrates a cross sectional view of an ultrasonic scanner for acatheter of some embodiments.

FIG. 8 illustrates a cross sectional view of yet another ultrasonicscanner for a catheter of some embodiments.

FIG. 9 illustrates a one dimensional CMUT array for a catheter of someembodiments.

FIG. 10 illustrates a two dimensional CMUT array for a catheter of someembodiments.

FIG. 11 illustrates a subassembly of a ring shaped CMUT array for acatheter of some embodiments.

FIG. 12 illustrates a subassembly of a ring shaped CMUT array for acatheter of some embodiments.

FIG. 13 illustrates a method of manufacturing a ring shaped CMUT arrayfor a catheter of some embodiments.

FIG. 14 illustrates a method of integrating various components of a CMUTequipped catheter of some embodiments.

FIG. 15 illustrates another method of integrating various components ofa CMUT equipped catheter of some embodiments.

FIG. 16 illustrates a wafer from which various components of a CMUTequipped catheter can be fabricated.

DETAILED DESCRIPTION

Various embodiments provide ultrasonic scanners which are positioned atthe distal ends of catheters. More particularly, some embodimentsprovide ultrasonic scanners equipped with side looking and forwardlooking capacitive micromachined transducer (CMUT) arrays at theirdistal ends.

Though piezoelectric transducers (PZTs) can perform some desirablediagnostic functions, it remains difficult to obtain piezoelectrictransducers (PZTs) with small form factors. More specifically, due toconstraints associated with the materials from which PZTs aremanufactured, it remains difficult to design and manufacture catheterswith PZTs small enough to fit within many catheters designed to benavigated through various cardiovascular vessels, neurovascular vessels,and other biologic structures. Moreover, PZT materials do not lendthemselves well to relatively high frequency regimes. For example, it isdifficult to design and manufacture a PZT capable of operation in theregion near (and above) 20 MHz which is useful for imaging biologicaltissues.

Furthermore, to form cylindrical arrays of PZT (such as the cylindricalarrays desirable for inclusion on various catheters) the individual PZTsmust be diced from flat sheets of the transducers. The individual PZTscan then be arranged in a cylindrical array on the catheter. As aresult, some of the individual PZTs (or groups thereof) can be damagedor contaminated with kerf or other contaminants during the dicing andassembly operations. Additionally, the dicing operation and the assemblyof the individual PZTs on to the catheter can lead to variations in theoperational characteristics of the individual PZTs. Thus, previouslyavailable PZTs have found use in only certain ultrasound applications.This disclosure provides CMUT based ultrasonic transducers, andcatheters equipped with such CMUTs which address at least some of theshortcomings of PZTs. As discussed herein, the ultrasonic transducersand catheters disclosed herein also possess other advantages.

CMUTs transmit and detect acoustic waves in adjacent media using twoplate-like structures arranged to form a capacitor. The plates (orelectrodes coupled to the plates) can be repetitively charged todisplace one plate relative to the other thereby generating the acousticwaves. Typically, an alternating current (AC) charges the plates. In thealternative, the plates may be charged to a selected voltage (with, forexample, a direct current or DC signal) and can be used to senseacoustic waves which impinge on the exposed plate and therefore displacethat plate relative to the other plate. The displacement of the exposedplate causes a change in the capacitance of the CMUT. The resultingelectric signal generated by the CMUT can be analyzed to generate imagesof the media surrounding the CMUT. Some CMUT based ultrasonic scannersinclude switches so that, when the switch is in one position, the switchallows the CMUT to transmit acoustic waves and, when the switch is inthe other position, the switch allows the CMUT to detect acoustic waves.

CMUTs can be fabricated separately or can be fabricated in various typesof arrays. For instance, a one dimensional (1-D) array of CMUTs can befabricated wherein the various CMUTs are formed in a linear array. 2-DCMUT arrays can also be fabricated in which the various CMUTs are formedin various patterns including, for example, rows and columns. The rowsand columns can create arrays which are generally square, rectangular,or other shapes. Moreover, individual CMUTs can be operated separately;can be operated in conjunction with other CMUTs; or can be operated inconjunction with all of the CMUTs in a particular array or scanner. Forinstance, the signals driving the various CMUTs can be timed to operatea number of the CMUTs as a phased array to direct the acoustic energy ina particular direction(s).

CMUT arrays can be formed to be flexible so that the array can conformto a surface, cavity, etc. with a desired or given shape or curvature.For instance, CMUT arrays can be fitted to conform to the shape of aparticular instrument, catheter, or other device. Similarly, the ICs (orother electronic circuits) used to drive the CMUTs (and sense thesignals there from) can be formed to be flexible also. Furthermore, theCMUTs and ICs can be integrated with each other and the instrument atthe same time using the same techniques or at separate times using thesame (or different) techniques as disclosed herein.

More particularly, the CMUTs and ICs of some embodiments can beintegrated with each other and a flexible membrane at the same timeusing semiconductor or micro electromechanical systems (MEMS)fabrication and packaging techniques (hereinafter “semiconductor”techniques). The flexible membrane, with the CMUTs and ICs on it, can bewrapped onto a catheter (or other device) to form a catheter with a CMUTbased ultrasonic scanner. These CMUT based ultrasonic scanners can beforward looking, side looking, or combinations thereof. In someembodiments, other transducers (e.g., pressure, temperature, etc.) canbe fabricated and integrated with the CMUTs and ICs on the flexiblemembrane.

FIG. 1 illustrates a cross sectional view of a catheter of someembodiments. The catheter 100 includes an ultrasonic scanner 110 whichcomprises a CMUT transducer 111, various electronics 112, a flexible andelongated body 120, a cable 130, connection wires 131, a lumen 140, aflexible distal tip 150, and an outer cover 160. The catheter 100typically also includes a handle at the proximal end of the elongatedbody 120. The handle allows surgical personnel with, or without,navigation aids to steer the distal tip 150 through vessels (e.g.cardiovascular vessels) within a patient's body. The distal tip 150 canbe coupled to the distal end of the elongated body 120 and can beflexible enough that it guides the distal end of the elongated body 120through the vessel without affecting the walls of the vessel.

In addition, the distal tip 150 can include a smooth lead surface tofacilitate the passage of the elongated body 120 through the vessel.Outer cover 160 can also be provided over the elongated body 120 (andother portions) of the catheter 100 to facilitated the passage of theelongated body 120 through the vessel. Once the distal tip 150 reaches adesired site, instruments can be inserted through the elongated body 120and the distal tip 150 via the lumen 140 (which typically runs throughthe length of the elongated body). Advantageously, the catheter 100allows surgical personnel to perform ultrasonic diagnostics at the siteand to perform these surgical procedures with minimal discomfort for thepatient. Catheter 100 can also include one or more sensors, transducers,instruments, etc. for performing various diagnostic procedures at thedesired site.

The lumen 140 can couple the distal tip 150 to the elongated body 120 ofthe catheter 100. The lumen 140 can also provide a structure on whichthe ultrasonic scanner 110 (with the CMUT transducer 111 and theelectronics 112) can be mounted. Typically, the body of the ultrasonicscanner 110 and the body of distal tip 150 are flush with each other soas to present a smooth overall surface to the walls of the vesselthrough which catheter 100 might be navigated.

The CMUT transducer 111 can include one or more individual CMUTelements. The various CMUT elements can be arranged in an array withinthe CMUT transducer 111. Moreover, CMUT transducer 111 can be a sidelooking transducer or a forward looking transducer. In some embodiments,catheter 100 includes both side and forward looking transducers.

Wires 131 can carry electronic data and control signals between externalsupport electronics and the ultrasonic scanner 110. In some embodiments,the external support electronics can include a control station computerwith software to analyze the signals from the ultrasonic scanner and togenerate images of the tissue surrounding the ultrasonic scanner. Cable130 routes the wires 131 from the proximal end of the elongated body 120to the distal end of the catheter 100. At the distal end of theelongated body 120, the wires 131 can electrically connect to theelectronics 112. Furthermore, interconnects (not shown) can electricallyconnect the electronics 112 and the CMUT transducer 111. The wires 131can provide electrical power to the electronics 112. In turn, theelectronics 112 can power the CMUT transducer 111 and provide a switchor switches arranged to cause the CMUT transducer 111 to switch betweentransmitting and detecting acoustic waves.

From the CMUT transducer 111 electronic signals indicative of thedetected acoustic waves can travel to the electronics 112 via theinterconnects. The electronics can perform certain functions (e.g.,filtering, signal conditioning, etc.) on these electronic signals. Theelectronics 112 can send the electronic signals to external supportingelectronics (not shown) via the wires 131. In some embodiments, thesupporting electronics includes a computer which is configured toanalyze the electronic signals and derive various images there from. Thewires 131 can therefore provide an interface between the electronics 112(and the CMUT transducer 111) and the supporting electronics.

When it is desired for the CMUT transducer 111 to transmit acousticwaves, the electronics apply an AC signal to the CMUT transducer 111thereby causing it to generate the acoustic waves. Moreover, theelectronics 112 can be configured to apply an AC signal to the CMUTtransducer 111 which has a frequency on the order of 1-100 MHz. However,the electronics 112 can be configured to drive the CMUT transducer 111with AC signals having other frequencies as well. In the alternative,when it is desired for the CMUT transducer 111 to detect acoustic waves,the electronics 112 can apply a bias signal or a modulation signal tothe CMUT transducer 111 and sense the returned electronic signalresulting from the echoed acoustic waves.

With reference now to FIG. 2A, a cross sectional view of a side lookingultrasonic scanner 209 of some embodiments is illustrated. Ultrasonicscanner 209 includes an IC 220, a flexible member 230, a lumen 240 or ashaft 241 (herein after the lumen 240), a pair of wires 250, and anouter layer 260. The CMUT array 210, IC 220, and the flexible member 230(hereinafter a flexible subassembly 208) can be attached to the lumen240. The CMUT array 210 and IC 220 can be fabricated separately (ortogether) using semiconductor techniques and can be mechanically coupledto each other by the flexible member 230. Flexible member 230 can alsobe coupled to the end of the CMUT array 210 which is opposite the IC 220and vice versa. The flexible member 230 can provide electricalconnectivity between the wires 250, the IC 220, the CMUT array 210, andother components of the ultrasonic scanner 209 while allowing thesecomponents to move relative to each other during assembling.

The detailed portion of FIG. 2A illustrates the attachment of theflexible subassembly 208 to the lumen 240. The detailed portion of FIG.2A also illustrates various components of a particular CMUT element ofthe CMUT array 210. These components of the CMUT element include amembrane 211, an insulation layer 214, a substrate 215, a top electrode216, a conductive layer 231 (of the flexible member 230), an insulationlayer 232 (of the flexible member 230), and a via 233 (of the flexiblemember 230). Various semiconductor and MEMS materials (hereinafter“semiconductor” materials) can be used to fabricate the CMUT. Forinstance the membrane 211, insulation layer 214, substrate 215, and topelectrode 216 can be formed from silicon, doped silicon, metal, oxide,nitride, etc.

In some embodiments, the CMUT array 210 is a 1 dimensional CMUT array(which includes one row of CMUT elements, see FIG. 9). However, CMUTarray 210 can be other types of CMUT arrays. For instance, CMUT array210 can be a 1.5 dimensional CMUT array, a 1.75 dimensional CMUT array,or a 2 dimensional CMUT array (which includes 2 rows of CMUT elements,see FIG. 10). The CMUT array 210 can be a flexible CMUT array asdescribed in U.S. Provisional Patent Application No. 60/992,020 entitledENHANCED CAPACITIVE MICROMACHINED ULTRASONIC TRANSDUCERS, filed on Dec.3, 2007, by Huang which is incorporated herein as if set forth in full.In addition, or in the alternative, CMUT array 210 can include flexibleelements between the individual CMUT arrays therein as described in U.S.Provisional Patent Application No. 61/024,843 entitled PACKAGING ANDCONNECTING ELECTROSTATIC TRANSDUCER ARRAYS, filed on Jan. 30, 2008, byHuang which is incorporated herein as if set forth in full. Moreover,these types of CMUT arrays can be formed using semiconductor techniques.The IC 220 can be fabricated in a similar manner as described in theforegoing provisional patent applications and can therefore be flexiblealso. Thus, the subassembly 208 can be flexible enough to conform tovarious surfaces (including surfaces which exhibit compound curvature)including lumen 240. While the flexible subassembly 108 can be wrappedaround objects or rolled into a tube, a portion of a lumen, or a lumen,the flexible subassembly can be formed into other shapes (even thosewith compound curves). For instance, the flexible subassembly can berolled into a cylinder, a portion of a lumens, or a lumens. In contrast,it is impracticable to form a flexible PZT based ultrasonic scannerusing semiconductor techniques.

Regarding the flexible member 230, flexible member 230 can include oneor more insulation layers 232 and at least one conductive layer 231.These insulation layers 232 and conductive layers 231 can be fabricatedusing semiconductor techniques and can be fabricated with thicknesses ofas little as 1 micrometer. Accordingly, the separation betweeninterconnects within flexible member 230 can be as little as 1micrometer thereby increasing the interconnect density as compared topreviously available ultrasonic scanners (and more particularly,previously available PZT based ultrasonic scanners). Furthermore, if itis desired to increase the density of the interconnects within flexiblemember 230, additional insulation layers 232 and conductive layers 231can be formed in flexible member 230. The layers 231 and 232 of theflexible member 230 can be fabricated from materials which arecompatible with semiconductor techniques. For instance, the conductivelayer 231 can be made of aluminum, gold, etc. and can be formed byelectroplating, sputtering, evaporating etc. a metal or other conductivematerial onto an appropriate substrate. The insulation layer 232 can bemade of Parylene, polydimethylsiloxane (PDMS), nitride, polyimide orKapton, etc.

With continuing reference to FIG. 2A, the CMUT membrane 211 andsubstrate 215 can define the transducing cavity 213. The top electrode216 of the CMUT can be coupled to the membrane 211 and together with thesubstrate 215 (which can serve as the bottom electrode of the particularCMUT element shown in the detailed portion of FIG. 2A) can cause thedisplacement of the membrane 211. More particularly, an electric signalcan be applied across the top electrode 216 and the substrate 215 usingthe connectivity provided by the wires 250, the conductive layer 231,and the via 233 to arcuate the CMUT element thereby generating acousticwaves in the surrounding media

FIG. 2B illustrates a cross sectional view taken along the line 2B-2B ofthe ultrasonic scanner 209 of FIG. 2A. It will be understood by thoseskilled in the art that the CMUT elements of the CMUT array 210 canoperate satisfactorily without an acoustic matching or backing layers.Moreover, the CMUT array 210 can operate satisfactorily without afilling material between the lumen 240 and the CMUT array 210. Thus, theflexible CMUT array 210 can be wrapped directly on the lumen 240. Insome embodiments, the flexible CMUT array 210 can be rolled into acylindrical shape and can therefore serve as the lumen 240. Thus, aseparate lumen 240 need not be included in the ultrasonic scanner 209.In those embodiments in which the rolled up CMUT array 210 serves as thelumen, the CMUT array 210 can be dimensioned to match the diameter ofthe lumen included in the elongated body 120 (see FIG. 1) of thecatheter 100. Thus, the lumen in elongated body and the rolled up CMUTarray 210 can be coupled to form a continuous lumen throughout thelength of the catheter 100.

FIG. 3 is a flow chart illustrating a method of manufacturing anultrasonic scanner. The method 300 can include integrating the CMUTarray 210 and the IC 220 with the flexible member 230 at step 302. Insome embodiments, the CMUT array 210 and the IC 220 can be integratedwith the flexible member 230 at the same time and using the sametechniques. However, in some embodiments, the CMUT array 210 and IC 220can be integrated with the flexible member 230 at differing times usingdiffering techniques. At step 304, the integrated CMUT array 210, IC220, and flexible member 230 (as a subassembly 208) can be wrapped intoa cylindrical shape. Thus, the subassembly 208 can be wrapped around thelumen 240 or can form the lumen 240. In any case, the resultingultrasonic scanner 209 can be assembled on to the lumen 140 (see FIG. 1)of the catheter 100. The wires 131 of the catheter 100 can be connectedto leads on the flexible member 230 at step 306. At step 308 the outerlayer 260 can be applied to the ultrasonic scanner 209 to complete themanufacture of the CMUT based ultrasonic transducer 209. The outer layer260 can be made of, for example, PDMS, Parylene, polyethylene shrinktubing, polyethylene terephthalate (PET) shrink tubing, etc.

In contrast to the manufacture of a PZT based ultrasonic scanner, method300 can omit the dicing of PZT a disc on a flex. Method 300 can alsoomit the creation of acoustic matching and backing layers. Method 300can also omit the creation of a layer of filling material between theCMUT array 210 and the lumen 240. Moreover, manufacturing steps such asseparately integrating the CMUT array 210 and the IC 220 with theflexible member 230 can be combined, thereby yielding additional costsavings and improving quality control. Accordingly, method 300 can besimpler, with fewer steps, than methods of manufacturing PZT basedultrasonic transducers.

With reference now to FIG. 14 a method of manufacturing CMUT basedultrasonic scanners is illustrated in more detail than the method 300.More specifically, FIG. 14 illustrates a method of forming a flexiblesubassembly 1408. FIG. 14 illustrates a wafer 1400 with a device layer1401, a handling wafer 1402, an insulation layer 1403, several trenches1405, a CMUT array 1410, several ICs 1420, a flexible insulating layer1429, a flexible member 1430, a conductive layer 1431, and an insulationlayer 1432. Wafer 1400 can be a silicon-on-oxide (SOI) wafer used tofabricate the CMUT array 1410, the ICs 1420, or various combinationsthereof. Wafer 1400 can also be used to fabricate the flexible member1430 and to integrate the CMUT array 1410 and the IC 1420 with theflexible member 1430.

With reference now to FIG. 14.1, wafer 1400 can include the device layer1401, the handling wafer 1402, and the insulation layer 1403. The devicelayer 1401 can determine the thickness of the CMUT array 1410 and theICs 1420. In the alternative to using a SOI wafer for wafer 1400, asilicon wafer can be ground to the desired thickness and used in lieu ofwafer 1400. In some embodiments, the area of wafer 1400 which will hostthe ICs 1420 may be protected by a layer of appropriate masking materialduring certain steps of the method illustrated by FIG. 14. FIG. 14.1illustrates that a CMUT array 1410 can be fabricated on wafer 1400 usingvarious semiconductor fabrication techniques.

As illustrated by FIG. 14.2 various trenches or opening patterns 1405can be formed in wafer 1400. Trenches and patterns 1405 should be etchedto reach the insulation layer 1403 of the wafer 1400. Trenches orpatterns 1405 can be used to separate various CMUT arrays 1410, elementsof the CMUT array, ICs 1420, and other components from each other orfrom the rest of the device layer 1401. As with the other stepsillustrated by FIG. 14, appropriate semiconductor techniques can be usedto form trenches 1405. Furthermore, FIG. 14.3 illustrates that the ICs1420 can be fabricated on wafer 1400. If the area which hosts ICs 1420had been coated with a protective material, the protective materialcould be removed before the fabrication of the ICs 1420.

In some embodiments, the CMUT array 1410 is usually made of materialswhich can tolerate higher temperatures than those likely to beencountered during fabrication of the ICs 1420. Thus, fabricating theICs 1420 on the wafer 1400 after the CMUT array 1410 can result in asatisfactory subassembly 1408. Some embodiments allow the CMUT array1410 to be fabricated on the wafer 1400 after the fabrication of the ICs1420 as will be discussed with reference to FIG. 15.

With continuing reference to FIG. 14, the steps shown from FIG. 14.4 toFIG. 14.6 are exemplary process steps which can be used to form theflexible member 1430. In embodiments which employ these steps, theflexible member 1430 has at least one layer of insulation layer and atleast one layer of conductive layer. FIG. 14.4 illustrates that a layerof flexible insulating material (e.g. Parylene, polydimethylsiloxane orPDMS, polyimide, nitride, etc.) can be patterned and created on wafer1400 as the first insulation layer of the flexible member 1430. Flexibleinsulating layer 1432 can be created on wafer 1400 in any appropriatemanner. For instance, flexible insulating layer 1432 can be spin-coated,evaporated, sputtered, deposited, etc., on to the wafer 1400. Moreover,the patterning of the flexible insulating layer 1432 can be selected sothat the flexible insulating layer 1432 allows access to the electrodes,leads, contacts, etc. associated with the CMUTs 1410 and the ICs 1420.

In FIG. 14.5, the creation of the conductive layer 1431 of the flexiblemember 1430 on the wafer 1400 is illustrated. The conductive layer 1431can be patterned and deposited on the wafer 1400 by any appropriatetechnique and can be performed in a manner to allow the fabrication ofinterconnections between the CMUT array 1410, the ICs 1420, and othercomponents on wafer 1400. The conductive layer 1431 can be fabricatedfrom aluminum, gold, copper, titanium, etc. or other appropriatematerials by (for instance) deposition, evaporation, sputtering, etc. Asmay be desired to form the flexible 1430 with multiple insulation andconductive layers, additional conductive layers 1431 and insulatinglayers 1432 can be patterned and created on wafer 1400 to provideinterconnects, vias, and associated insulators for the components hostedby wafer 1400. Where more than one conductive layer 1431 and insulatinglayer 1432 is formed on wafer 1400, various devices such as capacitors,inductors, etc. can be formed therein.

If desired, an outer layer 1429 can be formed on wafer 1400. The outerlayer may be used as a protection layer and treated as an insulationlayer of the flexible member 1430. Usually, but not necessarily, theouter layer is bio-compatible. Outer layer 1429 is illustrated by FIG.14.6 and can be formed from a flexible insulating material such asParylene, PMDS, polyimide, nitride, etc. by various techniques. Thethickness, patterning, and material of outer layer 1429 can be selectedto provide protection for the subassembly 1408 from mechanical abuse, toelectrically and thermally isolate the ultrasonic transducer from itsenvironment, and to provide a smooth and relatively friction freesurface for the subassembly 1408 to present to the walls of variousvessels into which it might be inserted. After this step, in someembodiments, the flexible member 1430 has been formed on the wafer 1400to connect the IC(s) 1420 and the CMUT 1410 electrically andmechanically.

FIG. 14.7 illustrates that the flexible subassembly 1408 can be obtainedby the removal of the handling wafer 1402, the insulation layer 1403,and the rest of device layer 1402. Thus, the manufacturing methodillustrated by FIG. 14 can result in a subassembly 1408 which includesthe CMUT array 1410 and the ICs 1420 integrated with each other and withthe flexible member 1430. Thus, the CMUT array 1410 and the ICs 1420 canbe fabricated on, and integrated with, the wafer 1400 using the sametechniques.

With reference now to FIG. 15, another method of fabricating asubassembly 1508 is illustrated. In the method of FIG. 15, the CMUTarray 1510 is fabricated after the ICs 1520 are fabricated. FIG. 15.1illustrates that the ICs 1520 can be fabricated on the wafer 1500 beforethe CMUT array 1510. Then, as illustrated by FIG. 15.2, the CMUT array1510 can be fabricated on the wafer 1500. The techniques and materialsused to fabricate the CMUT array 1510 can include techniques andmaterials selected to not affect the ICs 1520. For instance, techniquesand materials involving temperatures which the ICs 1520 can tolerate canbe used to fabricate the CMUT array 1510. With continuing reference toFIG. 15, FIG. 15.3 illustrates that various separation trenches oropening patterns 1505 can be formed in the wafer 1500. The trenches andpatterns 1505 can be etched to reach the insulation layer 1503 of thewafer 1500. Thereafter, manufacturing of the subassembly 1508 can besimilar to that of subassembly 1408 as shown in FIGS. 14.4-14.7. Thus,the CMUT array 1510 can be fabricated on the wafer 1500 after the ICs1520 are fabricated on the wafer 1500.

While FIGS. 14-15 illustrate the CMUT arrays 1410 and 1510 and the ICs1420 and 1520 being integrated with the flexible member 1430 and 1530from the active side of the CMUT arrays 1410 and 1510, it is possible tointegrate these components 1410, 1420, 1510, and 1520 with therespective flexible members 1430 and 1530 from the inactive side of theCMUT arrays 1410 and 1510. If access from the inactive side is desired,then through wafer interconnections can be fabricated to provideinterconnectivity for the various components of the subassemblies 1408and 1508. If access is desired from the active side, then through waferinterconnection might are not necessary for that purpose since the CMUTscan be readily accessible.

FIG. 16 illustrates a method of some embodiments in which the insulatinglayer 1502 of wafer 1500 is replaced with a cavity. More particularly,FIG. 16.1 illustrates that the wafer can be formed with an embeddedcavity 1604, and the IC(s) 1620 and the CMUT(s) 1610 can be fabricatedon the substrate 1601 above the embedded cavities 1604. FIG. 16.2illustrates that trenches or opening patterns 1605 can be etched throughthe substrate layer 1601. Then, in some embodiments, the trenches oropening patterns 1605 may be filled with a material which can beselected to allow for the separation of the CMUTs 1610 and the ICs 1620.Thereafter, manufacturing of the subassembly 1608 can be similar to thatof subassembly 1408 as shown in FIGS. 14.4-14.7. At final step, theflexible subassemblies 1608 can be easily taken out from the wafer 1600directly from the front side of the wafer 1600. With regard to theforegoing methods described with reference to FIGS. 14-16, the flexiblemembers 1430, 1530, and 1630 can be formed on the inactive side of theCMUT arrays 1410, 1510, and 1630. Through wafer interconnection can alsobe provided, depending on whether access to the CMUT arrays 1410, 1510,and 1610 is desired from the active or inactive sides of the CMUTarrays.

Moreover, any of the foregoing methods can be used to fabricate thesubassemblies 1408, 1508, and 1608. However, other methods can be usedto fabricate the subassemblies 1408, 1508, and 1608. For instance,International Patent Application No. ______, entitled CMUT PACKAGING FORULTRASOUND SCANNER, filed on Dec. 3, 2008, by Huang, and which isincorporated herein as if set forth in full describes additional methodsof fabricating the subassemblies 1408, 1508, and 1608. InternationalPatent Application No. ______, entitled CMUT PACKAGING ANDINTERCONNECTION, filed on Dec. 3, 2008, by Huang, and which isincorporated herein as if set forth in full describes additional methodsof fabricating the subassemblies 1408, 1508, and 1608.

As discussed with reference to FIGS. 14-16, the subassembly 208, whichincludes the CMUT array 210 (see FIG. 2), the ICs 220, and the flexiblemember 230, can be created using semiconductor techniques. Additionally,the CMUT array 210 and the IC 220 can be integrated with the flexiblemember 230 at the same time if desired. Similarly, if desired, multiplesubassemblies 208 can be integrated at the same time. Once integrated,subassembly 208 can be wrapped around, and attached to, lumen 240 tocreate ultrasonic scanner 209. Thus, relatively simple ultrasonicscanners 209 can be fabricated and assembled at lower cost and withbetter quality control than previously possible. Moreover, the methodsof manufacturing ultrasonic scanners disclosed herein enjoy theeconomies of scale offered by the semiconductor techniques used therein.

With reference now to FIGS. 4-8 various ultrasonic scanners 409, 509,609, 709, and 809 are illustrated. More particularly, FIG. 4 illustratesa cross sectional view of a side looking ultrasonic scanner 409 of someembodiments. The CMUT array 410 and IC 420 of the ultrasonic scanner 409can be integrated with the flexible member 430 from the inactive side ofthe CMUT array 410. Accordingly, ultrasonic scanner 409 can include oneor more through wafer interconnections 418. Through waferinterconnections 418 can provide electrical connectivity to the CMUTelements of the CMUT array 410 from the back side of CMUT substrate. TheICs 420 can be electrically interconnected with the CMUT elements fromtheir inactive surfaces through the flexible member 430. FIG. 4 alsoillustrates that the flexible member 430 (with the CMUT array 410 and IC420 thereon) can be wrapped around the lumen 440. Otherwise, themanufacture of the ultrasonic scanner 409 of FIG. 4 can be similar tothat of the ultrasonic scanner 209 of FIG. 2.

Now with reference to FIG. 5, a cross sectional view of a forwardlooking ultrasonic scanner of some embodiments is illustrated.Ultrasonic scanner 509 can include a ring-shaped CMT array 510 in lieuof, or in addition to, a side looking CMUT array (such as CMUT array410). The ring shaped CMUT array 510 can be positioned at the distal endof the ultrasonic scanner 509 with its active surface pointed in adistal direction. As described in more detail herein, subassembly 508(including ring shaped CMUT array 510) can be fabricated as onestructure and can be integrated from its active side. In thealternative, ring shaped CMUT array 510 can be fabricate as two or morecomponents and assembled into a ring shaped array. More particularly, asdiscussed with reference to FIGS. 11 and 12, the integrated subassembly508 can be folded inward at a location proximal to the CMUT array 510 topoint the elements of the CMUT array 510 in the distal direction asshown.

FIG. 6 illustrates another embodiment of a forward looking ultrasonictransducer 609. Ultrasonic transducer 609 includes a ring-shaped CMUTarray 610 which was integrated from its inactive side. Accordingly, CMUTarray 610 includes through wafer interconnects 618 to electricallyconnect the CMUT array 610 to the IC 620. Additionally, as discussedwith reference to FIGS. 11 and 12, the integrated subassembly 608 befolded outward (in contrast to ultrasonic scanner 509 in which thecorresponding subassembly 508 is folded inward) at a location proximalto the CMUT array 610 to point the elements of the CMUT array 610 in adistal or forward direction

A front view of an ultrasonic scanner 709 which is similar to theultrasonic scanner 509 (see FIG. 5) is illustrated in FIG. 7. Due to theinward folding of the CMUT array 710, the CMUT array 710 is shown beingpositioned closer to the lumen 740 than the flexible member 730.Ultrasonic scanner 609 is similar to ultrasonic scanner 509 in thisregard except that a portion of the CMUT array 710 can be positionedfurther from the lumen 740 than the flexible member 730. However, bothultrasonic scanner 509 and ultrasonic scanner 609 are expected to havesimilar operating characteristics.

Referring now to FIG. 8, a cross sectional view of an ultrasonic scannerof some embodiments is illustrated. In some embodiments the ultrasonicscanner 809 can include both a side looking CMUT array 810A and aforward looking CMUT array 810B. Additionally, the ultrasonic scanner809 can integrate other sensors 870 (such as a pressure sensor, atemperature sensor, etc.) with various CMUT arrays 810 and electronics(e.g. IC 820) without departing from the scope of the disclosure. Thus,some embodiments provide multifunction ultrasonic scanners 809.

With reference now to FIGS. 11-13, various embodiments of subassemblies1108, 1208, and 1308 of CMUT arrays, ICs, and flexible member areillustrated. These subassemblies 1108, 1208, and 1308 can be used toform ultrasonic scanners and, more particularly, forward lookingultrasonic scanners. For instance, FIG. 13 illustrates a process ofmanufacturing a forward looking ultrasonic scanner 1309. FIG. 13illustrates that the subassembly 1308 (including the one-dimensionalCMUT array 1310, the IC 1320, and the flexible member 1330 integrated ina generally planar configuration) can be used to manufacture a forwardlooking ultrasonic scanner 1309 with a ring shaped CMUT array 1310.Moreover, FIG. 13 illustrates that the CMUT array 1310 can be foldedthrough about 90 degrees relative to the plane defined by thesubassembly 1308 and as indicated by reference arrow 1336. Thesubassembly 1308 can then be rolled into a cylindrical shape asindicated by reference arrow 1338. Thus, the forward looking ultrasonicscanner 1309 can be formed from the generally planar subassembly 1308.

With reference now to FIG. 11, a subassembly 1108 with a 1 dimensionalCMUT array 1110 and which can also be used to form a forward lookingultrasonic scanner with a ring-shaped CMUT array. More particularly,FIG. 11 illustrates that subassembly 1108 can be generally planar andcan include the flexible member 1130 with the CMUT array 1110 and the IC1120 integrated therewith. CMUT array 1110 can be circular and can liein, or parallel to, a plane defined by the flexible member 1130.Flexible member 1130 can include one or more arcuate arms 1132 whichmechanically couple the CMUT array 1110 and the IC 1120 and provideelectrical connectivity between the same components. The CMUT array1110, the IC 1120, and the arms 1132 can define a void 1134 which canallow arms 1132 sufficient freedom of movement so that the arms 1132 canconform to the cylindrical shape of, for example, a lumen. Arms 1132 canbe mirror-images of each other as illustrated.

To form a ring-shaped CMUT array from subassembly 1108, the subassembly1108 can be rolled into a cylindrical shape while circular CMUT array1110 is folded inwardly. Thus, as the subassembly 1108 is rolled intothe cylindrical shape, the CMUT array 1110 can be folded through about90 degrees so that the CMUT elements of the CMUT array 1110 pointforward (or in a distal direction). In some embodiments, such as thosewhere the CMUT array 1110 is integrated from the inactive side (andtherefore includes through wafer vias), the CMUT array 1110 can befolded outwardly instead of inwardly.

Note that the arcuate arms 1132 can be shaped and dimensioned so thatthey lie flat against an appropriately shaped and dimensioned lumen whenthe subassembly is assembled to the lumen. In the alternative, when thesubassembly 1108 forms the shaft or lumen, the arcuate arms 1132 areshaped and dimensioned so that they generally conform to the cylindricalshape of the rolled up subassembly 1108. In any case, the rolled upsubassembly 1108 can be positioned on the distal end of an appropriatelyshaped lumen. In the alternative, when the subassembly 1108 forms thelumen, the rolled up subassembly 1108 can form the lumen of a catheter.

With reference now to FIG. 12 another subassembly 1208 is illustrated.More specifically, FIG. 12 illustrates that subassembly 1208 can alsoinclude a pair of arms 1232 and a pair of semi-circular CMUT arrays1210. Arms 1232 can be generally straight as opposed to the arcuate arms1132 of FIG. 11. While FIG. 12 illustrates the CMUT arrays 1210 as eachdefining a half circle, the CMUT arrays 1210 need not be identical. Forinstance, one CMUT array 1210 could define a larger portion of a circlewith the other CMUT array 1210 define a smaller portion of a circle. Inany case, the subassembly can be rolled into a cylindrical shape withthe CMUT arrays 1210 being folded over to form a forward lookingultrasonic scanner 1209.

CMUT based ultrasonic scanners provide several advantages over PZT basedultrasonic scanners. These advantages arise, in part, from therelatively low acoustic impedance of CMUTs. CMUTs typically have loweracoustic impedances than air, water, tissue, etc. As a result, andunlike PZTs, CMUTs can be used without a layer of material to match theacoustic impedance of the CMUTs with the acoustic impedance of thesurrounding media.

PZTs also transmit acoustic energy (i.e., acoustic waves) from boththeir front and rear surfaces. As a result of this characteristic, PZTsrequire a backing layer on their rear surface to absorb the acousticenergy emitted there from. Otherwise the acoustic waves transmitted fromthe rear of the PZTs could reflect from various structures and interferewith the operation of the PZTs. However, in absorbing the acousticenergy transmitted from the rear of the PZTs, the backing layersgenerate heat. As a result, PZTs can become warm, or even hot, duringoperation thereby reducing their desirability for use in certainapplications such as applications requiring their use with catheters.Since CMUTs transmit acoustic energy only from there front surfaces,heating due to misdirected acoustic energy is not a concern for CMUTbased ultrasonic scanners. Furthermore, the backing layers (and acousticmatching layers discussed previously) complicate the manufacturing ofPZT based ultrasonic scanners. In contrast CMUT based ultrasonicscanners can omit these layers and the attendant manufacturing steps.

Moreover, CMUT based ultrasonic scanners can be produced usingsemi-conductor manufacturing techniques. Since these semiconductortechniques benefit from decades of investments by various portions ofthe semiconductor industry, these techniques can provide relatively highlevels of uniformity, precision, repeatability, dimensional control,repeatability, etc. in the CMUTs thereby produced. Further still, manyof the foregoing semiconductor techniques can be batch processes. As aresult, economies of scale associated with these techniques allow forlower per unit costs for CMUT based ultrasonic scanners, particularlywhen relatively large volumes of ultrasonic scanners may be desired. Forinstance, since all of the features of the CMUT arrays on a particularwafer can be patterned simultaneously, the fabrication of multiple CMUTarrays introduce no (or little) overhead as compared to the fabricationof a single CMUT array.

Additionally, since CMUT based ultrasonic scanners can be produced withsemiconductor techniques, integrated circuits (ICs) and othersemiconductor devices can be integrated with the CMUT arrays withrelative ease. Thus, the CMUT arrays and the ICs can be fabricated onthe same wafer at the same time using the same techniques. In thealternative, CMUTs and ICs can be integrated into various transducers atdifferent times. Furthermore, CMUTs and ICs can be fabricated from thesame, or similar, biocompatible materials.

In contrast, the fabrication and integration of PZTs with othercomponents (e.g., ICs) using semiconductor techniques is impracticabledue to constraints imposed by the PZT materials Moreover, the availablePZT related fabrication and integration techniques suffer from severaldisadvantages including being labor intensive, being expensive, beingsubject to manufacturing variations, etc. Furthermore, available PZTtechniques meet with additional difficulties as the size of theindividual PZT devices approaches the small dimensions (e.g., tens ofmicrons) required for relatively high frequency devices. For instance,separation of the individual PZT devices is dominated by lapping anddicing techniques which lead to device-to-device variability.

Accordingly, CMUT based ultrasonic scanners enjoy both performance andcost advantages over PZT based ultrasonic scanners. More particularly,since it is typically desirable for ultrasonic scanners to havetransducers with both high frequency operating ranges and small physicalsizes, CMUT based ultrasonic scanners can have several advantages overPZT based ultrasonic scanners.

First, CMUT based ultrasonic scanners can be fabricated with betterdimensional control than PZT based ultrasonic scanners. Moreparticularly, CMUT based ultrasonic scanners can be fabricated withminimum dimensions less than about 1 micrometer whereas the minimumdimensions of PZT based ultrasonic scanners are greater than about 10micrometers. Accordingly, CMUT based ultrasonic scanners can befabricated with correspondingly smaller CMUT element pitches. Secondly,the minimum width and pitch of CMUT based ultrasonic scannerinterconnects can be less than about 2-3 micrometers whereas the minimuminterconnect width and pitch for PZT based ultrasonic scanners isgreater than about 25 micrometers. Thus, CMUT based ultrasonic scannerinterconnects can be fabricated at higher densities than PZT basedultrasonic scanner interconnects. Accordingly, CMUT based ultrasoundscanners can possess more transducers (for a given scanner size) or canbe smaller (for a given number of transducers) than PZT based ultrasonicscanners.

Moreover, given the improved device size of CMUT based ultrasonicscanners, as compared to PZT based ultrasonic scanners, CMUT basedultrasonic scanners can be created which can operate up to about 100MHz. In contrast, PZT based ultrasonic scanners are limited to operatingregions well below 20 MHz. Furthermore, since the resolution of anultrasonic transducer depends on its operating frequency, CMUT basedultrasonic scanners can be fabricated with correspondingly improvedresolution. For similar reasons, the bandwidth of CMUT based ultrasonicscanners is wider than the bandwidth of PZT based ultrasonic scanners.Accordingly, CMUT based ultrasonic scanners can be applied to moresituations than PZT based ultrasonic scanners.

The simpler design and fabrication of CMUT based ultrasonic scanners (ascompared with PZT based ultrasonic transducers) also gives rise tocertain advantages. For instance, since the ICs used to support theCMUTs and the CMUTs themselves can be fabricated with the sametechniques, fabrication of the CMUTs and ICs, taken together, can besimplified. Additionally, because CMUTs do not require matching orbacking layers, the manufacturing steps associated with these layers canalso be eliminated. Likewise, steps associated with integrating theCMUTs and the ICs can be eliminated or, if not, simplified.

The present disclosure is described with reference to specificembodiments thereof, but those skilled in the art will recognize thatthe present disclosure is not limited thereto. Various features andaspects of the above-described disclosure may be used individually orjointly. Further, the present disclosure can be utilized in any numberof environments and applications beyond those described herein withoutdeparting from the broader spirit and scope of the specification. Weclaim all such modifications and variations that fall within the scopeand spirit of the present disclosure. The specification and drawingsare, accordingly, to be regarded as illustrative rather thanrestrictive.

1. A method of manufacturing a catheter-based medical device comprising:integrating an electrical circuit with a flexible member; integrating anultrasonic transducer with the flexible member, the integratedelectrical circuit, the ultrasonic transducer, and the flexible memberbeing a flexible subassembly; shaping the flexible subassembly to be theultrasonic scanner; and attaching the ultrasonic scanner to thecatheter.
 2. The method of claim 1 wherein the ultrasonic transducer isflexible.
 3. The method of claim 1 wherein the electronic device isflexible.
 4. The method of claim 1 further comprising integrating theelectronic device and the ultrasonic transducer on a device layer of asubstrate before integrating the electronic device and the ultrasonictransducer with the flexible member.
 5. The method of claim 4 furthercomprising forming a least a patterned opening through a device layer ofa substrate.
 6. The method of claim 5 further comprising forming thedevice layer with at least one embedded cavity.
 7. The method of claim 4further comprising forming the device layer on a SOI wafer.
 8. Themethod of claim 1 further comprising integrating the electronic deviceand the ultrasonic transducer with the flexible member at the same time.9. The method of claim 1 wherein the integrating the ultrasonictransducer includes using a semiconductor technique.
 10. The method ofclaim 1 wherein the shaped flexible member defines at least a portion ofa lumen.
 11. The method of claim 1 wherein the integrating of theflexible transducer is from the side of the ultrasonic transducer whichincludes an active surface of the flexible ultrasonic transducer. 12.The method of claim 1 further comprising attaching the shaped flexiblemember to a lumen.
 13. The method of claim 1 wherein the flexibleultrasonic transducer includes at least one capacitive micromachinedultrasonic transducer (CMUT).
 14. The method of claim 1 furthercomprising folding a portion of the flexible member which hosts theflexible ultrasonic transducer wherein the folded portion of theflexible member and the flexible ultrasonic transducer form a forwardlooking ultrasonic transducer.
 15. The method of claim 1 wherein theflexible ultrasonic transducer includes at least a portion of a circularCMUT array.
 16. The method of claim 1 wherein the flexible memberincludes a pair of arms.
 17. A catheter-based medical device comprising:an electronic circuit; an ultrasonic transducer; a flexible member withthe electronic circuit and the ultrasonic transducer integrated therewith, the integrated electronic circuit, the ultrasonic transducer, andthe flexible member being a flexible subassembly, the flexiblesubassembly being shaped to be the ultrasonic scanner; and a lumen towhich the ultrasonic scanner is attached.
 18. The catheter-based medicaldevice of claim 17 wherein the ultrasound transducer is a flexibleultrasound transducer.
 19. The catheter-based medical device of claim 17wherein the shaped flexible subassembly defines a portion of a lumen.20. The catheter-based medical device of claim 17 wherein the flexibleultrasonic transducer includes a through wafer interconnect.
 21. Thecatheter-based medical device of claim 17 wherein the ultrasonictransducer includes at least one CMUT element.
 22. The catheter-basedmedical device of claim 17 wherein the ultrasonic transducer is a CMUTarray including at least two CMUT elements.
 23. The catheter-basedmedical device of claim 17 further comprising one of a temperaturesensor or pressure sensor integrated with the flexible member.
 24. Thecatheter-based medical device of claim 17 wherein the ultrasonictransducer includes at least a portion of a circular CMUT array.
 25. Thecatheter-based medical device of claim 17 wherein the ultrasonictransducer is a forward looking ultrasonic transducer.
 26. Acatheter-based medical device comprising: an integrated circuit; acapacitive micromachined ultrasonic transducer (CMUT); and a flexiblemember with the integrated circuit and the CMUT integrated there with,the integrated circuit, the CMUT, and the flexible member being aflexible subassembly, the flexible subassembly being shaped to functionas an ultrasonic scanner and at least a portion of a lumen, the CMUTbeing positioned on the distal end of the ultrasonic scanner and being aforward looking ring shaped ultrasonic transducer.
 27. A method offabricating a catheter-based medical device comprising: fabricating thesemiconductor device on a substrate which defines a separation layeradjacent to the semiconductor device; separating the semiconductordevice from the substrate by forming a pattern of openings in thesubstrate, around the semiconductor device; and to a depth sufficient toreach the separation layer; integrating an electrical circuit with aflexible member; integrating an ultrasonic transducer with the flexiblemember, the integrated electrical circuit, the ultrasonic transducer,and the flexible member being a flexible subassembly, wherein thesemiconductor device includes at least one of the electrical circuit orthe ultrasonic transducer; shaping the flexible subassembly to be anultrasonic scanner; and attaching the ultrasonic scanner to thecatheter.
 28. The method of claim 27 wherein the semiconductor device isselected from the group consisting of a CMUT element, a CMUT array, anintegrated circuit (IC), or a combination thereof.
 29. The method ofclaim 27 wherein the separation layer defines an embedded cavity.